Solar cells that are transparent enough to be used to tint windows on buildings or cars, have been developed by U.S researchers.

Conventional solar cells are bulky and rigid but lightweight cells are usually far less efficient. However, a new method of making the silicon-based devices could create thin, flexible cells without any trade-offs.

Brittle wafers of silicon are sliced into ultra-thin pieces and carefully 'printed' onto a malleable surface. The cells are so flexible they can be rolled around a pencil.